1. Correct usage:

Karen, you should take a cruise to Alaska.

In this case, "you" refers to the person addressed in the sentence.

2. Incorrect usage:

Paying out of pocket for health insurance is a cost you don't budget for.

Who does "you" refer to in this sentence? If you are talking about a specific group of people, explicitly state who you are referring to:

Paying out of pocket for health insurance is a cost (who?) don't budget for. (average people? working people? students?)

3. Correct the use of you in these sentences:

A. If you apply to college, you must include your academic history.

B. When you create a business plan, you need to include revenue and expenditure projections.

C. You're never going to get the needed affection from a cat; that's why dogs are better pets.

D. Buying books online allows you to save money.